1. Field of the Invention
The present invention relates to a digital camera composed of a lens unit having a taking lens and a solid state imaging device, and a camera body to which the lens unit is removably attached.
2. Description Related to the Prior Art
Digital cameras are widely used, and include a solid state imaging device such as a CCD image sensor for capturing an image to store data of the image to a data storage. Digital cameras in which a lens unit having a taking lens and a solid state imaging device is removably attached to a camera body are also known.
Among such digital cameras, some allow both remote photographing and normal photographing. In the remote photographing, photographing is performed while the lens unit is detached from the camera body, and the data is exchanged wirelessly between the lens unit and the camera body. In the normal photographing, photographing is performed while the lens unit is attached to the camera body (for example, Japanese patent laid-open publication Nos. 10-117302, 10-243277 and 11-298770, and U.S. Pat. No. 6,052,509 corresponding to Japanese patent laid-open publication No. 9-261519).
The digital cameras disclosed in the above publications are composed of a lens unit having a solid state imaging device incorporated therein, and a camera body to which the lens unit is removably attached. The camera body processes and stores image data, and also displays the image. These digital cameras have a wireless communication device for sending and receiving data via radio waves between the lens unit and the camera body. The digital cameras are capable of the remote photographing by sending and receiving image data and control signals via radio waves. Since there is no restraint of a cable, such digital cameras are easier to handle than the digital cameras in which the lens unit and the camera body are connected through the cable.
In the digital cameras disclosed in the above publications, however, communication speed of the wireless communication is generally slower than that of wired communication. Therefore, the communication speed becomes insufficient when large volumes of image data are obtained by the lens unit per unit time, such as during high speed continuous shooting of still images or high definition movie shooting. There is another problem in that the data transmission has to be performed with extremely wideband frequency.
Moreover, the wireless communication has lower stability as compared to the wired communication. Therefore, when noise occurs during the transfer of movie data, the data transfer momentarily stops, and the movie data having defect may be recorded in a recording medium of the camera body.
The data communication can also be performed by wired communication through connection contacts such as mount portions or slots when the lens unit is attached to the camera body. Accordingly, the disadvantage of slow communication speed can be improved by switching to the wired communication when the lens unit is attached to the camera body. However, such solution of merely switching the communication system brings another problem that the wireless communication device is wasted when the lens unit is attached to the camera body.